On Wednesday, 11 March 2020 at 05:25:43 UTC, kookman wrote:
I am using libpcap to read from stored pcap files, and want to
use std.bitmanip.bitfields to read TCP flags from the file,
using a struct like:
struct TcpHeader {
align(1):
ushort srcPort;
ushort dstPort;
uint seqNo;
uint ackNo;
mixin(bitfields!(
bool, "flagFin", 1,
bool, "flagSyn", 1,
bool, "flagRst", 1,
bool, "flagPsh", 1,
bool, "flagAck", 1,
bool, "flagUrg", 1,
bool, "flagEce", 1,
bool, "flagCwr", 1,
bool, "flagNs", 1,
ubyte, "reserved", 3,
ubyte, "dataOffsetWords", 4 // in 32bit words, min=5,
max=15
));
ushort windowSize;
ushort checksum;
ushort urgentPtr;
this(inout ubyte[] bytes)
{
srcPort = bytes.read!ushort();
dstPort = bytes.read!ushort();
seqNo = bytes.read!uint();
ackNo = bytes.read!uint();
// now what? how to read bitfields??
}
const uint dataOffset() // convenience method to get
offset in bytes
{
return dataOffsetWords * 4;
}
}
How can I get at the private field behind the bitfields to read
into it. I'm using std.bitmanip.read because I need the network
order (bigendian) conversion for this data.
Actually, doing it a "smarter" way worked:
struct TcpHeader {
align(1):
ushort srcPort;
ushort dstPort;
uint seqNo;
uint ackNo;
mixin(bitfields!(
bool, "flagFin", 1,
bool, "flagSyn", 1,
bool, "flagRst", 1,
bool, "flagPsh", 1,
bool, "flagAck", 1,
bool, "flagUrg", 1,
bool, "flagEce", 1,
bool, "flagCwr", 1,
bool, "flagNs", 1,
ubyte, "reserved", 3,
ubyte, "dataOffsetWords", 4 // in 32bit words, min=5,
max=15
));
ushort windowSize;
ushort checksum;
ushort urgentPtr;
this(inout(ubyte)[] bytes)
{
import std.traits: FieldNameTuple;
static foreach (f; FieldNameTuple!TcpHeader) {
pragma(msg, f);
__traits(getMember, this, f) =
bytes.read!(typeof(__traits(getMember, this, f)));
}
}
const uint dataOffset() // convenience method to get
offset in bytes
{
return dataOffsetWords * 4;
}
}